The present invention relates to the field of dental restoration, more precisely to a process for the retraction of sulcus according to the independent claims.
For a preparation of a dental prosthesis, an impression of the teeth and the part of the jaw adjacent to these teeth must be provided to the dental technician. Especially, a correct impression of the sub-gingival area of the tooth is important in dental restoration. Therefore, an impression of the dental situation has to be prepared by the dentist. In order to cover the transitional area of tooth and jaw, it is necessary to free the neck of the tooth which is covered by the gingiva. Thus, for preparing the dental impression, the sulcus must widened, i.e. the sulcus and/or the gingival must be retracted and the neck of the tooth be exposed.
Beside a widely. used method which relies on the insertion of a retraction cord into the sulcus, U.S. Pat. No. 5,676,543 describes an alternative method: A mold of the dental situation is prepared by a curable molding mass. The cured impression is subsequently removed. A layer of a syringable and curable material is applied into the mold and the thus prepared mold is placed onto the teeth again. Mandatory, the syringable and curable material needs to contain an astringent or a substance causing tissue retraction. By exerting pressure onto the mold, the curable material is pressed in the area between the neck of the tooth and the gingiva. Due to the hemostatic compound and the hydrostatic pressure of the silicone, a tissue contraction is caused, and the sulcus retracts from the neck of the tooth. A proper impression of the dental situation including the uncovered sulcus can be made after cleaning. However, a major drawback in practice is that the application of the syringable, curable material into the negative dental impression not always leads to the required results. During the reinsertion of the mold, the syringable material is often substantially smeared so that a correct sulcus retraction is no longer guaranteed. Moreover, the contraction of the sulcus by the astringent is not always sufficient in order to guarantee the quality of the mold. Furthermore, the proper quantity of syringable material to be applied proves to be difficult to find since during application the contours of the negative mold are covered and thus no control of the layer thickness is longer possible. Besides the mentioned drawbacks, the necessity of providing an astringent unwantedly complicates the overall composition of the syringable material.
Another method of cordless retraction of gingival sulcus is disclosed in US 2004/0106086. Therein, in contrast to U.S. Pat. No. 5,676,543, a dental impression material is used for widening the gingival crevice adjacent to the tooth. The dental impression material may either be provided into a dental dam, and then the dental dam is placed over the teeth and adjacent gingival, or the impression material is firstly placed onto the tooth and gingival, and the dental dam is then placed on top of it. According to that invention, the dental dam is made of a porous foam or sponge type material, thereby facilitating subsequent removal of the dam together with the set impression material. A drawback of this technique is the dental dam, which is seated on adjacent teeth and therefore is not suitable for complicated dental situations. Moreover, a substantial content of an astringent is again, as in U.S. Pat. No. 5,676,543, to be contained in the impression material in order to assure retraction of the gingival.
US patent application 2004/0265777 discloses a different approach of gingival retraction by suggesting retraction devices which may be inserted into the gingival sulcus in a single motion by direct transmission of vertical forces circumferentially through the rigidity of a structural backing component to laterally displace the gingival tissue around a tooth. This approach, however, is hampered by the fact that the gingival tissue is likely to be harmed by inserting the device directly into the crevice of tooth and gingival.
Yet another method of sulcus retraction is disclosed in EP 1 459 701 A1, wherein firstly an impression mold is taken and the impression mold subsequently removed, secondly a silicone material is applied onto the boundary of sulcus and tooth, which silicone material expands upon curing. Upon reinsertion of the impression mold after appliance of the silicone material, the silicone material expands into the gingival crevice and widens it. However, this two-step approach of impression molding and retraction of sulcus is relatively time-consuming. Alternatively, the use of hollow cotton rolls is suggested in WO 2004/082510; however, sufficient direction of the expanding silicone material into the sulcus can not be achieved with any dental situation by using such cotton rolls.
A further approach for the retraction of gingival margins is disclosed in EP 92 329, using foam silicone material. According to EP 92 329, the complete tooth and surrounding gingival tissue is covered by the silicone material, and may be held in place by a carrier such as a spoon. As the expansion of the silicone material is thereby only insufficiently directed into the sulcus, no satisfactory sulcus retraction is however achieved in practice.
The object of the invention is to avoid the disadvantages of the prior art, especially to provide an alternative method and cap for uncovering the neck of a tooth by retraction of sulcus, which is more convenient for the patient, less time-consuming and more reliable. This problem is solved by a method, a cap and a dental kit according to the features of the independent claims.